This invention relates to novel adhesive films useful for bonding, particularly useful for bonding artificial fingernails to natural fingernails. Adhesives currently used for such purposes consist of an adhesive film covered on both sides by release papers. Release papers are silicon coated papers that substantially do not stick to the adhesive film.
The current adhesive used in tabular form to adhere plastic artificial fingernails to the natural nail is a 0.005 inch unsupported laminating film (9472 product of 3M). It is in the class of pressure sensitive adhesives generally described as acrylic based. Although this material in general gives good results, there still are a large number of nails which fall off before the intended removal time. The reasons for this are varied and not known for certain.
Due to the difficulties in making coherent adhesive films we are not aware of any commercial adhesive of this type that is substantially thicker than 0.006 inches. This is a critical point as explained below.
An excellent summary of the known prior art in this area can be found in the 3M selection guide for Scotch laminating adhesives, etc. A suitably tacky products for the nail adhesive tab application is listed in this brochure as 9472 (an acrylic based item), in fact this is the product that is used in the most popular prior art adhesive tab. As can be seen from page 17, this material has high adhesion to plastic surfaces. It is a single 5 mil thick film "stabilized" with randomly dispersed glass fibers. These fibers are intended to prevent oozing of the film during die-cutting. Due to manufacturing difficulties it has not been possible to obtain a substantially thicker film in spite of the fact that that severely limits the utility of even that material as a nail adhesive. During the efforts to overcome these problems, we were able to obtain a 10 mil film of "Isotack" laminating film (a #600 series product) from 3M. This material has much less initial tack (and consequently is easier to form in manufacturing). However, this 10 mil thick material did not prove suitable as a nail tab adhesive material becaues of its low initial tack.
Thus, with conventional laminating film technology, it has not proven possible to make an adhesive better than the one currently being used, and better adhesives are among the objectives of this patent.
Double coated adhesives which contain an imbedded carrier film are known. The nature of the carrier film can be varied, but usually takes the form of tissue or a thin plastic sheet. These double coated adhesives can have a single adhesive. Also, they have been constructed with different adhesives on either side of the carrier layer for joining dissimilar surfaces. The construction claimed in U.S. Pat. No. 4,511,608 is an example of a system employing a carrier film tab coated with adhesive in both of its sides.
We have found that it is not possible to solve the problem of premature nail dislocation with the state of the art double coated carrier film adhesives, for three reasons:
a. This first problem is essentially the same as that for unsupported films. Double coated adhesives that contain a flexible carrier film (no more than approximately 0.003 in) and in addition have a suitably tacky adhesive system are not available, to the best of knowledge, in net adhesive thickness greater than 0.008 in. After a certain thickness, which our experience suggests is around 0.003 inches, the carrier film will become so thick and inflexible that the double coated system is completely unsuitable as a nail adhesive. However, having a suitable flexible carrier film again limits the thickness of adhesive that can be applied. Adhesive thickness is even more limited when the adhesive in question is the relatively low viscosity tacky type needed for nail adhesion. Thus there are no commercially available double coated adhesives, which are suitable for nail adhesion, and none which have a net adhesive thickness of greater than 0.008 inches as required in this invention.
b. Any carrier film will partially limit the easy conformability of the adhesive to the natural nail and artificial nail surfaces, even flexible films as defined above which do allow a reasonable measure of nail adhesion. This makes them less effective than otherwise similar unsupported films.
c. Thirdly, with double coated adhesives any adhesive which extends beyond the free edge of the natural nail becomes very difficult to remove. Thus it is difficult to avoid having free adhesive material lodged under the artificial nail causing unsightly soiling problems. Thus, any carrier in an artificial nail bonding system is very detrimental to product use, and so the improved systems of the present invention do not use any double coated adhesives technology.
It has been shown, however, that the uniquely thick (at least 8 mils) and tacky constructs of this invention do give a completely satisfactory adhesion of the plastic to the natural nail.
The foregoing problems of the prior art have been substantially solved by the present invention and it is to be expected that the adhesive film of this invention will be readily accepted in the artificial fingernail art.